It's part of the "eco-school" program in Gud-Chantier, a village in Senegal's Fouta region along the country's border with Mauritania.

VOA: standard.2010.04.01

And it would,you'd get a clear blister-like region, it would turn pustular.

你会看到一个透明的像水泡一样的地方,它会变成脓疱

耶鲁公开课 - 生物医学工程探索课程节选